1. Field of the Invention
The present invention relates to a needle plate, and more particularly to a needle plate for use in a sewing machine which provides a seam as a result of relative movement between the sewing machine and a sewing material holder.
2. Description of the Related Art
A needle plate of this general type is known from German Provisional Patent AS 16 60 928. The known needle plate is intended for a sewing machine for the production of a seam, in which the material to be sewn is clamped between two clamping plates of a cloth holder. The needle plate has a needle-plate attachment, which is provided with a needle hole, extends over the top of the needle plate, and is supported for rotating around an axis of rotation at the plane of movement of the sewing needle, from the operating position into a position which does not extend over the top of the needle plate. In the known needle plate, the needle-plate attachment serves to compensate for the difference in height between the needle plate and the top edge of the lower clamping plate of the cloth holder so that the cloth is not pulled downward by the perforating needle. On the other hand, as a result of the outwardly swung position of the needle-plate attachment, it is possible to replace or transfer the cloth holder without lifting it above the plane of the needle-plate attachment which extends into the cloth holder during the sewing. The disadvantage of the known needle plate is that its sole needle-plate attachment has a constant sewing level. This level is defined by the distance which is determined by a fixed point, for instance, the point of swing of the needle-plate attachment, and the upper edge of the needle-plate attachment which serves as a resting surface for the cloth. A prerequisite for the dependable formation of a seam is, as is known, that the bottom side of the cloth being sewn is supported, when a needle-plate attachment which extends over the needle plate is used, by the upper edge of said attachment so that fluttering of the cloth does not occur upon the penetration of the needle. If thicker regions, due for instance to folds or small parts such as slide fasteners, strips of material or the like, are present on the main part of the cloth within the course of the seam, particularly on the bottom side of the cloth, the position of the upper edge of the needle-plate attachment must correspond to the maximum thickness which occurs. This means, however, that those places which do not have thick regions in the sewing-material part are not supported by the needle-plate attachment, so that flutter-free sewing of cloth provided with partial thick regions which is clamped in a cloth holder is not possible with the known needle plate.